1. Field of the Invention
The present invention relates to an electric-circuit board and a display apparatus having the board.
2. Description of the Related Art
An electric-circuit board in which wiring-pattern paths can be selected as desired has been used in various fields. It is also used in a liquid-crystal display apparatus for sending various types of signals.
A liquid-crystal display apparatus 1 which is configured as shown in FIG. 1 has a liquid-crystal display device (liquid-crystal panel) P. The liquid-crystal display device P includes a pair of glass substrates 2 and 3 disposed oppositely to each other and clamping liquid crystal. On each of these glass substrates 2 and 3, transparent electrodes are disposed in a matrix. The glass substrates 2 and 3 are configured in different shapes such that the glass substrate 2 is wider than the glass substrate 3 at the upper and lower edges in FIG. 1 and the glass substrate 3 is longer than the glass substrate 2 at the left edge. At the glass-substrate edges where only one glass substrate appears, transparent electrodes formed on the corresponding glass-substrate surfaces are exposed.
Tape automated bonding films (hereinafter called TABs) 5, each of which supports IC 53 for driving liquid crystal serving as driving means, are connected to the exposed portions of the transparent electrodes. As a result, IC53s and TABs 5 for driving the liquid crystal enclose the liquid-crystal display device P at three sides. As shown in detail in FIG. 2, a TAB 5 for driving the liquid crystal has a flexible base-film section (film carrier) 50 made from polyimide resin or the like, and input terminal sections 51 and output terminal sections 52 are formed by wiring patterns made by copper foil or the like on the base-film section 50. Between these terminal sections 51 and 52, IC53 for driving the liquid crystal is tape-automated-bonded. IC53 converts a signal from the input terminal sections 51 to the signal having the specified waveform and outputs the signal to the liquid-crystal display device P through the output terminal sections 52. The output terminal sections 52 on a TAB 5 are electrically connected to the liquid-crystal display device P with, for example, anisotropic electrically-conductive film. With the anisotropic electrically-conductive film being clamped by the exposed electrodes of the liquid-crystal display device P and the output terminal sections 52, thermal crimping is performed to assure electrical conduct.
The input terminal sections 51 of TABs 5 for driving the liquid crystal are connected to a printed circuit board (PCB) 6 by soldering. A control unit not shown sends a power signal and control signals through the PCB 6 to the TABs 5 for driving the liquid crystal and the TABs 5 for driving the liquid crystal applies the signal having the specified waveform to the liquid-crystal display device P to display various types of information.
The configuration of the PCB 6 will be described next by referring to FIG. 3.
The PCB 6 is configured by three laminated base members 61, 62, and 63 made from insulating materials such as glass epoxy. On the surfaces of the base members 61, 62, and 63, wiring patterns 65, 66, and 67 are formed by copper foil having a width of 5 to 20 .mu.m on the first to third layers. The first-layer wiring pattern 65 is used as a land pattern to mount the PCB to the TABs 5. The second-layer wiring pattern 66 is used for applying a power signal to the TABs 5. The third-layer wiring pattern 67 is used for applying control signals to the TABs 5. These wiring patterns 65, 66, and 67 are formed such that they are short to reduce the wiring-pattern resistance. Each wiring pattern is connected to each other by through holes (not shown) made on the base members.
The PCB 6 is deformed due to thermal expansion of the wiring pattern 67 as the ambient temperature rises because the thermal expansion rate of the wiring pattern 67 made of copper foil or the like is larger than that of the base member 61, made from glass epoxy. The inventors found that this deformation was caused by wiring patterns.
As shown in FIG. 3, the first-layer wiring pattern 65 and the second-layer wiring pattern 66 are formed symmetrically against the center lines vertically according to the circuit configuration, and the third-layer wiring pattern 67 is not formed symmetrically against the center line vertically. The PCB 6 used for this liquid-crystal display apparatus has a longitudinal shape.
As the ambient temperature rises the lower half of the base member 63 expands where the wiring pattern 67 is disposed and the upper half of the base member 63 expands little where the wiring pattern 67 is not disposed, resulting in a warp in the Y direction in the PCB 6 as shown in FIG. 4A. In some cases, a warp occurs in the thickness direction (Z direction) as shown in FIG. 4B. This warp is a problem especially for a display panel having a 15-inch or larger display screen, since the PCB 6 is required to be long.
Such a warp makes soldering between the PCB 6 and the TABs 5 in the manufacturing process of the liquid-crystal display apparatus complicated. It becomes difficult to align the input terminal sections 51 of the TABs 5 to the wiring pattern 65 (land pattern for mounting the TABs 5) of the PCB 6, resulting in long positioning work or disabling the soldering itself.